At the present time, the great majority of single-level disks that are rewritable once use a technique based on organic colorant. The structure of a disk in accordance with the prior art is shown in FIG. 1.
These disks are generally constituted of an optical stack comprising:                a transparent substrate 1 consisting of e.g., plastic, polycarbonate;        a colorant layer 2 sensitive to the writing wavelength;        a reflecting layer 3 formed, e.g., by an alloy of gold or silver; and        one or two protection layers 4.        
The data is written in a spiral form on the disk surface by focusing a high-power diode laser 5 on the colorant layer through the substrate so that in the end it is represented by an alternation of non-written high-reflection zones and written low-reflection zones. The data is read with a low-power diode laser. This is made possible for reading as well as writing by the presence of a pre-etched groove on the plastic substrate.
Active layers based on organic materials are described, e.g., in U.S. Pat. No. 4,940,618 or EP 353 393. However, weak transmission of the organic colorants prevents stacking several rewritable levels. It is then necessary to turn to an inorganic solution.
The state of the art also includes 1) materials belonging to the family of cermets, a known term for designating metallic ceramic combinations deposited by the projection of a dielectric material and 2) one or several metallic elements.
For example, U.S. Pat. No. 4,640,860 discloses a process for manufacturing such a disk using cermets. However, the type of layer does not permit realization of high-density recording supports because the cermet layers have absorption and reflection rates that are too high to allow for multilayer structures.
Similar solutions are disclosed in JP 56-156942 that describes a disk having a film of the cermet type on a cylindrical support. The writing surface is increased, but such a support is not compatible with the readers generally used.
It would therefore be advantageous to provide recording supports with a high density of information on supports that can be used with standard reading equipment.